ON THE LOAD-BEARING POWER OF SILICEOUS REFRACTORIES AT HIGH TEMPERATURES
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The softening behavior under load of 5 series of siliceous bricks prepared experimentally with usual factory processes at a silica-brick plant has been examined by means of an Endell's apparatus. The first series consisted of semi-Dinas bricks made of soft quartzite of Buzen and Fukushu clay and containing 96.6 to 44.1% of silica; test-pieces for the load-test were small cubes cut from the bricks; besides load-test, linear expansion up to 800°C, residual expansion shown on heating at cone 19 to 20 for 4 hours, and refractoriness have been measured. The second series comprised silica bricks made of 7 different quartzites and fired to cone 17; testpieces were cubic as above; P. C. E. has also been determined. The third series contained small cylindrical silica refractories which were made of Dairen quartzite ground to varying fineness but were prepared with fixed amounts of lime and water, a same forming pressure, and a same firing temperature, i.e. cone 17; also true sp. gr., porosity, and compressive strength have been tested. Test-pieces of the fourth series were small cylindrical silica bricks made of "Akashiro" quartzite of Tamba with addition of 0 to 8% of lime; P. C. E., porosity, true sp. gr., and compressive strength have been determined. The fifth series comprised small cylindrical silica bricks made of the Tamba quartzite with forming pressures varying from 50 to 400kg. per sq. cm.; they have also been examined for bulk density, porosity, and compressive strength. The results of the experiments seem to justify the following conclusions:-(1) The softening temperature of semi-Dinas bricks rises with increasing contents of silica. Although an increase of silica causes an increase of thermal expansion, it serves in reducing residual contraction.(2) Owing to only slight variation in silica contents of usual silica bricks made of different quartzites and also to the intricate influences of impurities of quartzites, silica bricks with high contents of silica don't have always high softening temperatures.(3) The influence of the variation in the fineness of quartzite-grain upon the softening temperature of silica brick under load is not intense except when the grain is so fine as for instance its mean diameter is 0.25mm.(4) The softening temperature of silica brick made of sole quartzite is strikingly higher than that of the brick bonded with any amount of lime. However there is no remarkable difference among the softening temperatures of the bricks containing 1 to 4% of lime. It has also been ascertained from an experiment of the present paper and from former experiments made by a silica-brick plant that silica bricks with up to 4% of lime give almost similar results in refractoriness-test, slag-corrosion test, and open-hearth furnace test. In other words, it is likely that any addition of lime up to 4% is not detrimental to the quality of silica brick.(5) Any low forming pressure results a silica brick yielding at a low temperature under load. However the pressures over 150kg. per sq. cm. are only slightly effective in improving the softening behavior and moreover give no particular superiority in porosity, bulk sp. gr., and mechanical strength at ordinary temperatures. 150kg. per sq. cm. are probably the most economical forming pressure for commercial products.
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公益社団法人 日本セラミックス協会 | 論文
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